During this, the X-51A’s fourth and final planned flight, the unmanned WaveRider vehicle was carried beneath the wing of a B-52H and dropped from an altitude of about 50,000 feet over the Pacific Ocean off southern California. A solid rocket booster fired and propelled the cruiser to scramjet takeover, creating the supersonic environment necessary to operate the engine. The scramjet successfully propelled the cruiser more than 230 nautical miles in approximately six minutes, streaking through the sky from Mach 4.8 to Mach 5.1 while climbing in altitude. The engine ran full duration, depleting all fuel as planned. It was the longest of the four X-51A test flights and the longest air-breathing hypersonic flight ever. Early indications show the propulsion system accomplished all objectives.

The X-51A Waverider prepares to launch its historic fourth and final flight. The cruiser achieved Mach 5.1 traveling 230 nautical miles in just over six minutes, making this test the longest air-breathing hypersonic flight ever.Image Credit: Bobbi Kapka, U.S. Air Force